WBPA
Whole Body Phase Angle (50 kHz)
Phase angle is an electrical quantity in degrees describing the relationship between reactance and resistance measured as current passes through the body — a value for following a trend, not a grade for your health.
Short answer
Phase angle is a directly measured electrical property of your tissue rather than a calculated estimate — that is where its value lies. The manufacturer gives no reference range for it, though, so a single number has nothing to be related to. What is usable is following its development in yourself under comparable conditions and reading it next to the ECW Ratio. It is not a grade for your health.
- Resistance (R)The opposition of body fluids to the passing current.
- Reactance (Xc)The delay of the current at cell membranes, which behave like a capacitor.
- Impedance (Z)The total opposition of the body — resistance and reactance combined, the hypotenuse of the triangle.
- Phase angle (φ)The angle between resistance and impedance. It is calculated from R and Xc, not measured directly.
What the value represents
Most values on the result sheet are the output of a calculation: the device measures the electrical properties of tissue and estimates kilograms of water, muscle or fat from them using equations. Phase angle is a different case. It is that electrical property itself, expressed in degrees. It passes through no body composition model.
The current the device sends through the body meets two different kinds of opposition. Resistance (R) is the opposition presented by body fluids. Reactance (Xc) is the opposition arising at cell membranes — they behave like tiny capacitors and hold the current back for a moment. That delay is the physical basis of phase angle.
Phase angle is the angle between these two components: it is calculated as the arctangent of reactance divided by resistance. The larger the reactance relative to resistance, the larger the phase angle. Put practically: if membranes hold the current back more markedly, the angle is larger; if it passes without much delay, the angle is smaller.
A fundamental caveat is required here. The manufacturer manual gives no reference range for phase angle — neither a general one nor one by age and sex. You therefore have no manufacturer-defined boundary that would let you say this value is fine. Phase angle is a legitimate measured quantity, but one without manufacturer-defined bounds. What makes sense is following its development in yourself rather than comparing a single number with a table from the internet.
- The angle between impedance and resistance, in degrees, measured at 50 kHz for the whole body.
- The relationship between reactance (the opposition arising at cell membranes) and resistance (the opposition of body fluids).
- According to the manufacturer, reactance is related to cell mass and to the structural integrity and functional state of the cell membrane. The manual states that strengthening the membrane and its structural function raises phase angle, while damage or reduced function lowers it.
- It does not represent a grade for health, fitness, biological age or cell quality as a whole. It is not a score and it has no upper or lower bound set by the manufacturer.
- It does not represent the amount of any body component. It cannot be converted into kilograms of muscle or fat, or litres of water.
How the value is produced
- A measured value. Phase angle is derived directly from the resistance and reactance measured as a weak alternating current passes through the body. The reference documentation classes it among directly measured quantities, not among estimates or calculations.
- The relationship is phase angle = arctan(reactance ÷ resistance). Impedance is the vector sum of resistance and reactance, and all three quantities form a trigonometric relationship.
- The whole-body value is reported at 50 kHz. The device measures phase angle at three frequencies — 5, 50 and 250 kHz — and takes 15 phase angle readings in total, that is three frequencies for each of the five segments.
- Impedance is measured at eight frequencies from 1 kHz to 3 MHz, in 40 readings altogether (eight frequencies × five segments). Phase angle uses the three frequencies listed above.
- Reference comparison: on the Evaluation Result Sheet a T-score and a Z-score against the manufacturer data set are shown for whole-body phase angle at 50 kHz. The T-score compares with a young age group, the Z-score with the same age group. The manufacturer states that this data set affects only the evaluation, not the analysis result itself.
- Age, sex and ethnicity do not enter the calculation. They affect only the reference evaluation and scores.
How to read the current value
- Do not look for an in-range or out-of-range band here. The manufacturer manual gives no reference range for phase angle, so the result sheet carries no recommended span for it the way it does for fat, BMI or the ECW Ratio.
- Do not import thresholds from articles, tables or marketing material. Phase angle depends on the measurement frequency, the type of device and the population measured; a number from one source does not automatically apply to a measurement on another device.
- The only comparison the manufacturer offers for this value is the T-score and Z-score on the evaluation sheet. They describe position relative to the manufacturer reference set, not to a health norm, and the manufacturer itself states that chart settings can differ by country.
- A single value without context therefore says almost nothing. Usable information appears only from a series of measurements under comparable conditions.
- Neither a lower nor a higher number is a finding in itself. The manual describes the direction of influence (strengthening the membrane raises the angle, damage or reduced function lowers it) but does not state from which value a problem begins.
- Phase angle is not a grade for health or the result of a fitness test. It is not a score and it has no defined ceiling to aim at.
- Values from different frequencies are not interchangeable. Whole-body phase angle is reported at 50 kHz; segmental values at 5 and 250 kHz are different quantities and are not compared with it.
How to read change over time
- The trend is the main — and, given the absent reference range, practically the only — usable information here.
- Always compare the same frequency (50 kHz for the whole body) and measurements taken under comparable conditions: similar time of day, no training or sauna immediately beforehand, similar fluid intake.
- Take seriously only a repeated shift in the same direction across several measurements. A difference between two visits can easily arise from differing measurement conditions alone.
- When phase angle moves, look at the ECW Ratio and at intracellular water at the same time. Phase angle and the distribution of water between the inside and outside of cells are closely linked, so the values often move together.
- Do not read a change in phase angle as a change in health status. It is a shift in the electrical properties of tissue whose cause the measurement does not establish.
- On the Comparison Result Sheet the manufacturer shows phase angle for the current and previous measurement side by side. That is the intended use of this value.
General principles: how to read change between measurements →
What to read it with
- The ECW Ratio – the most closely related value. The distribution of water between the inside and outside of cells feeds into phase angle directly.
- Intracellular water (ICW) – related to the amount of cells; according to the manual a rise in ICW means a rise in cell mass.
- Body Cell Mass (BCM) – the indicator the manufacturer recommends particularly where fat free mass may be distorted by excess extracellular water.
- The ECM/BCM ratio – completes the view of the balance between the cellular and extracellular components.
- Segmental phase angle – shows whether the whole-body value rests evenly on all segments.
- Skeletal Muscle Index – the amount of muscle, which phase angle does not establish but which is often followed alongside it.
- Impedance and reactance – the quantities phase angle arises from directly.
Common misunderstandings
- Phase angle is not a grade for health. It is not a score, it has no scale from zero to a hundred and no manufacturer-defined target.
- There is no manufacturer-defined boundary for a good phase angle. The InBody 970 manual gives no reference range, so claims of the form below X degrees is bad have no support in the manufacturer documentation.
- Values from different devices are not interchangeable. Frequencies, electrode design and the measurement setup all differ.
- Values from different frequencies on the same device are not interchangeable either. 5, 50 and 250 kHz give different numbers with different meanings.
- Phase angle is not a measure of biological or metabolic age and does not convert into one.
- A higher number is not automatically a better result. The manual describes the direction of influence, not a ranking.
- Phase angle does not diagnose disease, malnutrition, oedema, inflammation or overtraining.
- Phase angle was not part of the manufacturer validation study against DEXA, so the accuracy conclusions reported for fat and fat free mass do not apply to it.
What can affect the result short term
- Hydration and the distribution of fluid between the inside and outside of cells — the most significant factor, because phase angle is an electrical property directly dependent on the state of tissues and fluids.
- Body position before the measurement: the manual recommends standing for at least 5 minutes, because moving from lying to standing lets gravity draw blood into the lower limbs.
- Training shortly beforehand, which changes perfusion and fluid distribution.
- The quality of electrode contact: dry hands and feet need wiping, otherwise electrical contact worsens and the measured impedance with it.
- Room temperature — the manual recommends 20 to 25 °C, because circulation changes in both cold and heat.
- Showering and sauna before the measurement, which likewise change circulation.
- Food and drink shortly before the measurement, and a full bladder.
- The menstrual cycle, during which the amount of body water fluctuates.
What to do next
The explanation of the value is the same for everyone. Only the suggested step changes — pick whichever fits you.
- Treat phase angle as an accompanying value you follow over time, not as a number you try to place in a band.
- Record your measurement conditions. For a value with no reference range, comparable conditions are the only guarantee that a trend means anything.
- When someone offers you a threshold for a healthy phase angle, find out which device, frequency and population it comes from. Without that the number is not transferable.
- Follow phase angle alongside the ECW Ratio and intracellular water. The three together give context the angle alone does not have.
- If the result worries you, or it shifts repeatedly alongside a worsening state of health, take it to a doctor rather than adjusting your training from a single number.
What the value does not determine
- The manufacturer gives no reference range for it, so a single value has nothing to be related to.
- It is not a grade for health, fitness or biological age.
- It does not diagnose disease, malnutrition, oedema, inflammation or overtraining.
- It is not comparable between different devices or between different frequencies on the same device.
- It does not express the amount of any body component and cannot be converted into kilograms or litres.
- It was not part of the manufacturer validation study against DEXA.
- It is sensitive to measurement conditions, because it is a directly measured electrical property of tissue.
On terminology
- Phase angle is a quantity, not a score. It has no target value and no ceiling.
- Calling it cell health or cell quality is a simplification. The manual speaks of the structural integrity and function of the cell membrane and describes only the direction of influence, not thresholds.
- Whole-body phase angle is always reported at 50 kHz. Without a stated frequency a phase angle value is ambiguous.
- The manufacturer nowhere labels any phase angle value as normal; it publishes no reference range for this quantity at all.
When to discuss it with a professional
Phase angle is not a diagnostic tool and is not meant for self-assessment of health. If it shifts repeatedly alongside fatigue, weight loss, swelling or other problems, that belongs with a doctor — the measurement itself cannot establish the cause.
In more depth, with sourcesIn more depth: the physics of phase angle and why it lacks a reference rangeExpand the detailed explanation
When alternating current passes through the body it meets two distinct kinds of opposition. Resistance (R) is the classic ohmic opposition presented by body fluids with dissolved ions. Reactance (Xc, capacitive reactance) arises at cell membranes: a membrane is a thin lipid bilayer between two conducting media, an arrangement that behaves electrically like a capacitor. A capacitor briefly holds charge and releases it with a delay, so current stops being in phase with voltage. The size of that phase shift is the phase angle. Formally, phase angle = arctan(Xc ÷ R), and impedance is the vector sum of both components; the manufacturer manual describes the same thing as the phase angle of a resistor and capacitor in series.
The choice of 50 kHz is not arbitrary. Low frequencies do not pass well through the membrane and reflect mainly extracellular water; high frequencies pass through and also capture intracellular water. At 50 kHz the current divides between the two paths such that measured impedance markedly reflects both the conducting medium and the capacitive behaviour of membranes — which is why 50 kHz has historically settled as the reference frequency of bioimpedance measurement and as the frequency the expert literature on phase angle refers to. InBody 970 measures impedance at eight frequencies from 1 kHz to 3 MHz (40 readings in total) and phase angle at three frequencies of 5, 50 and 250 kHz (15 readings in total), with the whole-body value reported at 50 kHz.
What sets phase angle apart from most other items on the result sheet is that it does not arise through a body composition model. Fat mass, muscle mass and basal metabolic rate are the output of regression relationships and assumptions about tissue hydration; phase angle is the ratio of two directly measured electrical quantities. It therefore does not inherit the uncertainty of the composition equations. Nor, however, does it inherit their interpretive frame: while the manufacturer publishes recommended ranges for fat, it gives no range at all for phase angle — neither in the result sheet manual nor in the device catalogue. The reference documentation for InBody 970 explicitly lists this among the figures the sources do not contain.
The expert literature does not fill that gap with a single universal threshold. The review by Norman and colleagues summarises phase angle as a parameter whose values differ by age, sex and body build, and whose meaningful use requires reference values matching both the population and the measuring device. Taking a single number from someone else table would therefore be misleading — not only because of the population, but because devices differ in frequencies, electrodes and measurement setup. The only comparison the manufacturer itself offers for this value is a T-score (against a young age group) and a Z-score (against the same age group) on the Evaluation Result Sheet, and explicitly only as an evaluation that does not affect the analysis result.
One defensible use follows: longitudinal tracking in one person on one device under standardised conditions. The manual is consistent with that in the construction of its Comparison Result Sheet, which shows phase angle for the current and previous measurement side by side, and in the Cole-Cole plot, whose axes carry resistance and reactance; the manufacturer reads a shift of the plot upwards along the reactance axis as a healthier cell membrane. At the same time, the manufacturer internal validation study against DEXA verified fat mass, fat free mass and segmental lean mass, not phase angle — so its accuracy is not documented by that study.
Sources
- InBody 970 Result Sheet Interpretation (ENG_A_211104) — InBody Co., Ltd.
- Bioelectrical phase angle and impedance vector analysis – clinical relevance and applicability — Clinical Nutrition
- Bioelectrical impedance analysis – part I: review of principles and methods — Clinical Nutrition (ESPEN guidelines)
- Bioelectrical Impedance Analysis – history and principles — NCBI Bookshelf
On this page
Related values
Related articles
Where to find it
Whole-body phase angle and segmental phase angle among the additional parameters.
- Reviewed by
- MojeInBody content team
- Date
An InBody measurement is not a diagnostic tool. Results do not determine health status and do not replace a medical examination.
FAQ
Frequently asked questions
Answers to what people ask most often about this value.
What is a good phase angle?
That question cannot be answered honestly with a number. The InBody 970 manual gives no reference range for phase angle, and the device catalogue sets no threshold either. The figures circulating in articles come from different devices, frequencies and populations and are not transferable. What is usable is following your own development under comparable conditions.
Is phase angle a measure of health or fitness?
No. It is an electrical quantity describing the relationship between reactance and resistance measured as current passes through the body. The manual gives only the direction of influence — strengthening the cell membrane and its structural function raises phase angle, damage or reduced function lowers it — but does not turn it into an assessment of health or a fitness test.
Why is phase angle reported at 50 kHz specifically?
At that frequency the current divides between the path through fluids and the path across cell membranes such that both components show markedly in the measurement. Fifty kilohertz is also the frequency most bioimpedance literature refers to. The device also measures phase angle at 5 and 250 kHz, but those values cannot be substituted for the whole-body one.
Why do I get a completely different phase angle on another device?
Phase angle depends on frequency, on the design and placement of electrodes and on the measurement setup. Values are therefore not interchangeable between devices. Comparison only makes sense between measurements from the same type of device under similar conditions.
How can I raise my phase angle?
The manufacturer gives no instructions for raising phase angle, and phase angle is not a goal in itself. The manual describes it as related to the structural integrity and function of cell membranes and to the ratio of water inside and outside cells. It is therefore more practical to follow it as an accompanying value next to muscle mass and the ECW Ratio than to try to train it directly.
What does it mean if my phase angle fell?
On its own it is not a diagnosis. Phase angle is sensitive to measurement conditions — hydration, time spent standing beforehand, recent training and electrode contact. Confirm that the measurements were comparable, and take seriously only a repeated shift in the same direction. Even that is a prompt for a conversation with a professional, not a conclusion.
What are the T-score and Z-score for phase angle on my result?
They show the position of your value relative to the manufacturer reference data set: the T-score against a young age group, the Z-score against the same age group. They are the only comparisons the manufacturer offers for phase angle, and they are an evaluation against manufacturer data rather than a health norm. The manufacturer also states that the settings of these charts can differ by country.
Explanations make the most sense alongside your own trend.
The public guide is open to everyone. The client portal adds your own value, history and the context of a specific measurement.